Basic Electricity and the Water Pipe Analogy
Let's start by first defining a few electronic parameters and compare them
to their water pipe counterparts. The Figure below shows that Voltage in
Electronics is similar to Water Pressure in a water pipe.
Voltage = Force that Moves Electrons (sometimes called the electromotive
force or EMF)
Pressure = Force that moves water (sometimes called pounds per square
inch or psi.)
Now lets look at another electronic parameter called current and compare it
to the flow of water in a water pipe. Current in Electronics is similar to
Water Flowing in the water pipe shown above.
Current in Electronics = A measure of electron movement (Amperes or
Amps is a measure of the number of negative charges per second that are
passing a given point in an electronic circuit)
Flow Rate = A measure of water movement (GPM or Gallons per Minute is
the measure of the amount of water that passes a given point in a
mechanical system each minute)
A few basic electronic components and their mechanical counterparts:
The Switch: Since you don't want to waste water when you are not using it,
you have a faucet or valve to turn the water on and off. Similarly, an
electronic switch turns the electricity on and off in an electrical circuit. A
switch connects ("on") or disconnects ("off") the wires in a circuit from the
battery or other voltage source. This removes ("off") or connects ("on")
the force that pushes the electrons through the wires in the electronic
circuits.
Figure 4
The Resistor: Why is the water pipe that goes to your kitchen faucet
smaller than the one that comes to your house? And why is it much smaller
then the main water pipe that supplies water to your entire town? Because
you don't need that much water! The pipe size limits the amount of water
you can get per minute ( Gallons per Minute or GPM ). Electricity works in a
similar manner, but wires have so little resistance they would have to be
super thin to limit the flow of those very, very tiny electrons. Water flow
through a pipe can also be restricted by filling the pipe with rocks. This
would reduce the gallons per minute that would pass through the pipe for
the same pressure at the input of the pipe. If the pipe was filled with sand it
would offer even greater Resistance to the flow of water. In electronics
there is a component called the Resistor that is the counterpart of the rock
and sand filled pipes. Resistors control how many electrons per second
can flow through the resistor for a given voltage across the resistor.
Electrical resistance is measured in ohms in honor of an electronic
scientist named George Simon Ohm (1787-1854). His formulation of the
relationship between current, voltage, and resistance is the basic law of
current flow. To increase the gallons per minute through a pipe you would
increase the pressure across the pipe or reduce the resistance of the pipe.
To increase the amps through a resistor you need to increase the voltage
across the resistor or reduce the value (ohms) of the resistor. This
phenomenon is known as "Ohm's Law". Mathematically Ohms law is
written as:
V=IR
Where V = Voltage, I = Current, and R = Resistance
Open circuits are the same as pinching a hose and preventing the water
from flowing. AN OPEN CIRCUIT IS NOT THE SAME AS AN OPEN WATER
PIPE! An open water pipe is equivalent to a short circuit because water
flows freely and the pressure drops to zero.